In The Lancet Psychiatry, Jesse Fann and colleagues report the long-term risk of dementia following traumatic brain injury (TBI) in a national population-based observational study. Using Denmark's enviable and societally accepted comprehensive register systems, the authors could link recorded inpatient and outpatient episodes of TBI with other registry records years and decades later for any type of dementia. This means that the analysis included 27 632 020 person-years of observation of 2·8 million people in 132 000 episodes of recorded TBI during a 36-year period between 1977 and 2013, with dementia outcomes being detected through the same systems for 127 000 of those people between 1999 and 2013...